This invention concerns a lighting or illumination device for a microscope, in particular a surgical microscope, of a type having at least one observation beam path, an illumination system, and a deflection device for deflecting light emitted from the illumination system onto an object to be observed, for example an eye to be operated on, the deflection device providing an illumination of the object under various illumination angles with regard to the at least one observation beam path.
Lighting devices for surgical microscopes generally use an illumination beam path featuring an angle of approximately 6° (so-called 6° illumination) with respect to the observation beam path. This avoids unwanted shadow formation which would arise in the case of greater angles between the observation beam path and the illumination beam path.
Eye surgery presents further specific requirements with respect to the illumination of a microscope. First of all, sufficient plasticity of the image is achieved with an illumination angle of again approximately 6°. However, for certain surgical ophthalmological observations or operations, it is necessary to produce the so-called red reflex. This involves the pupil of the operated eye being lit up red by light reflected from the retina. This type of illumination is of great significance for example in the case of cataract operations as residual tissue is particularly easy to detect in the back light of the red reflex. The generation of the red reflex requires smaller angles between the observation beam path and the illumination beam path; angles between 0° and 2° are preferable (so-called 2° illumination) here.
Surgical microscopes designed with two pairs of stereoscopic observation beam paths for one main surgeon and one co-observer often have a shortcoming in that, while the main surgeon is able to see the red reflex clearly, the co-observer's view of it is inadequate. Dependent upon his position, either to the right or left of the main surgeon, the co-observer only receives a good red reflex in one of his two observation channels. This interferes with the stereoscopic observation.
A lighting device for a surgical microscope with an illumination system positioned outside the optical axis of the microscopic lens and which illuminates the operation area parallel to the lens axis through the microscope objective, and with a deflection element on the side of the microscope objective facing away from the object, which illuminates the operation area with a fraction of the illuminative light along the objective axis is known from DE 040 28 605. This lighting device is characterised by the illumination system being fitted with a reflection element on the objective side reflecting the illuminating light parallel to the objective axis towards the objective of the microscope, and the deflection element illuminating the area of operation under an inclination angle with respect to the objective axis, this being smaller than the inclination angle under which the reflection element illuminates the area of operation. The greater inclination angle is preferably 6° in this instance, while the smaller one may vary between 0° and 6°.
The disadvantage of this design is that the rays reflected by the deflection element are boundary rays from the lighting aperture of the lighting system, so that an illumination close to the axis, for example under an angle of 2° to the observation beam path, leads to a relatively non-homogeneous and vignetted illumination of the luminous field.
Other lighting devices for surgical microscopes are known from DE 196 50 773 A1 and EP 1 109 046 A1. These lighting devices also use the boundary rays of the lighting device's lighting aperture for illumination close to the axis, leading to the disadvantages specified arising here as well.
Another disadvantage with the state-of-the-art technology is that the surgical microscopes described are designed to be relatively tall, as the 2° and the 6° illumination are arranged on top of each other.